Covers for electrochemical cells and related methods

ABSTRACT

Embodiments of the invention relate to an electrochemical cell system including a cover that affects reactant flow into an electrochemical cell array.

PRIORITY OF INVENTION

This non-provisional application claims the benefit of priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No.61/021,822, filed Jan. 17, 2008, which is herein incorporated byreference.

BACKGROUND

Electrochemical cell systems, such as fuel cell systems have beenidentified as attractive power supplies for a wide range ofapplications. Environmental conditions both surrounding the system andproximal to the system can influence the operation and performance ofelectrochemical cells. Favorable environments in proximity to theelectrochemical cells can improve cell performance. As examples,humidity, temperature, mass-transport of reactants, and pollutant orcontaminant levels present in the electrochemical cell can affectperformance of the cell.

Currently, sub-systems can be integrated into an electrochemical cellsystem to control operating parameters of the electrochemical cell andprovide desired conditions within the electrochemical cell. For example,in some fuel cell systems, external humidification systems, heaters andcooling loops, and reactant delivery pumps and flow fields exist foradjusting internal conditions of the fuel cell. Alternately, fuel cellsystems have been designed that minimize use of ancillary components byintegrating features for passive control of internal conditions. Forexample, fuel cells having planar architectures for fuel cells have beendeveloped that provide a passive breathing surface for receivingreactant. Water retention barriers can be used to manage waterevaporation from the fuel cells. Conventionally, water retentionbarriers include porous materials disposed over the active areas andimpermeable frames sealed around the perimeter of the fuel cells.

Active control systems can result in substantial parasitic power lossesand a larger overall footprint. Further, existing technologies whichattempt to passively control internal conditions still exhibit membranedehydration and significant performance losses. For fuel cells usingflow fields, overall performance can be low as a result of uneven watercontent and localized hot spots across the fuel cell even though a netself-humidifying environment may be possible. For planar fuel cellarchitectures, evaporation of water from passive breathing surfaces canstill cause membrane dehydration, and performance remains limited byinsufficient water content in the membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 illustrates a cross-sectional view of a prior art electrochemicalcell system.

FIG. 2 illustrates a cross-sectional view of an electrochemical cellsystem, including an off-set cover, according to some embodiments.

FIG. 3 illustrates a cross-sectional view of an electrochemical cellsystem, including an off-set cover with optional porous layer, accordingto some embodiments.

FIG. 4 illustrates a cross-sectional view of an electrochemical cellsystem, including an off-set cover with an optional porous layer,according to some embodiments.

FIG. 5 illustrates a perspective view of an electronic device powered byan electrochemical cell utilizing an off-set cover, according to someembodiments.

FIG. 6 illustrates a perspective view of an electronic device utilizingan off-set cover, according to some embodiments.

FIG. 7 illustrates a block flow diagram of a method of delivering areactant to an electrochemical cell array, according to someembodiments.

FIG. 8 illustrates a graphical view of modeling results of calculateddiffusion length versus gap height, according to some embodiments.

SUMMARY

Embodiments of the present invention relate to an electrochemical cellsystem. The system includes an array of electrochemical cells, includinga reactive surface, the surface having one or more active regions andone or more less-active regions in contact with the one or more activeregions. The system also includes a cover, including a transport layerhaving one or more transport barrier regions and one or more openedregions. The transport barrier regions are in proximity to the activeregions and the opened regions are in proximity to the less-activeregions.

Embodiments also relate to an electrochemical cell array cover includinga transport layer, including one or more transport barrier regions andone or more opened regions. The transport barrier regions overlay one ormore active regions of one or more electrochemical cells of anelectrochemical array.

Embodiments also relate to a method for operating an electrochemicalcell array, including contacting active regions of an electrochemicalcell array with a reactant fluid via opened regions in a cover andinhibiting a product fluid from being removed from the local environmentthrough use of the cover.

DETAILED DESCRIPTION

The Detailed Description includes references to the accompanyingdrawings, which form a part of the Detailed Description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated.

In the appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Also, in the following claims, the terms “including” and“comprising” are open-ended, that is, a system, device, article, orprocess that includes elements in addition to those listed after such aterm in a claim are still deemed to fall within the scope of that claim.Moreover, in the following claims, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

Embodiments of the invention relate to a cover for an electrochemicalcell array and related system. The present invention relates to a novelstructural relationship between active regions of an electrochemicalcell array and transport barrier regions integrated in a cover thatunexpectedly improves performance. Specifically, transport barrierregions of the cover are arranged in proximity to the active regions ofthe electrochemical cells to provide a transport shield between theactive regions and the external environment. The transport barrierregions may shield all or a portion of the active regions. In someembodiments, the electrochemical cell may be a fuel cell.

Conventionally, operation of electrochemical cells, such as fuel cells,at higher current densities typically favors increasing mass-transportto the active areas by opening or expanding regions in proximity toactive areas. However, embodiments of the present invention allow forsufficient reactant delivery to the active areas when using materialswith transport barriers between the active areas and the externalenvironment by instead providing an indirect flow pathway to the activeareas via less-active areas surrounding the active areas.

This indirect flow pathway can facilitate a microclimate or localenvironment that provides more favorable conditions across the activearea to improve performance of the fuel cells. This indirect flow pathmay effectively reduce transport to the active regions orthogonal to thereactive surface and increase transport to the active regions in-planeto the reactive surface and may further include tortuous flow through aporous layer. The indirect flow contacts all or only a portion of theperimeter of the active regions of the electrochemical cells.

The cover can be integrated in a housing of a portable device, forexample as described in commonly-owned U.S. Patent ApplicationPublication No. 2007/0090786, entitled “Devices powered by conformablefuel cells” and commonly-owned U.S. Patent Application Publication No.2006/0127734, entitled “Flexible fuel cells having external support”,the disclosures of which are herein incorporated by reference in theirentirety. The cover can be disposed on a passive reactant deliverysurface of the fuel cells. Architectures of fuel cells may be planar,although the covers can conform to any suitable architecture. Examplesof such fuel cells can be found in commonly owned U.S. PatentApplication Publication No. 2005/0250004, entitled “ELECTROCHEMICALCELLS HAVING CURRENT-CARRYING STRUCTURES UNDERLYING ELECTROCHEMICALREACTION LAYERS,”, and commonly-owned U.S. patent application Ser. No.12/238,241, entitled “Fuel cell systems including space-saving fluidplenum and related methods”, filed Sep. 25, 2008, the disclosures ofwhich are herein incorporated by reference in their entirety. Materialsincluded in the cover can include combinations of conductive andnon-conductive materials.

DEFINITIONS

As used herein, “reactive surface” refers to a surface of anelectrochemical cell array in which all or a portion of anelectrochemical reaction is supported or carried out.

As used herein, “active region” refers to reactive areas in contact withor integrated into a reactive surface of an electrochemical cell or cellarray. The active regions support all or a portion of an electrochemicalreaction. The active regions may include one or more catalysts,conductive or non-conductive materials or gas-diffusion layers, asexamples.

As used herein, “less-active region” refers to an area in contact withor integrated into a surface of an electrochemical cell or cell array inwhich no electrochemical reactions occur or are supported or only anegligible amount occurs or is supported. Less-active regions mayinclude current collectors, structural support members or insulatinggaps.

As used herein, “transport layer” refers to a region in anelectrochemical cell cover providing a flow path for a reactant flow.The reactant flow may be actively or passively moved through the flowpath. The transport layer may include transport barrier regions andopened regions, for example.

As used herein, “transport barrier region” refers to materials orcomponents that impede, affect, or block transport mechanisms. Thetransport barrier regions may be a mechanical cover and may besubstantially or fully impermeable to air or water, or a fuel cellreactant (e.g. fuel) for example. For example, the mechanism impeded,affected, or blocked may be any combination of transport mechanismsincluding water evaporation from the active areas (e.g. due to reducedconvective fluid flow over the active regions), fully or partiallydemobilized water vapor, heat transfer (direction independent) betweenthe active regions and the external environment, reduced influx ofpollutants and/or contaminants (for example CO, NH₃, NO_(x), VolatileOrganic Compounds, salts), current transfer (or lack thereof) from theactive areas, etc. These mechanisms can provide other beneficialconditions such as increased relative humidity in the electrochemicalcell, membrane hydration, higher operating pressures, higher limitingcurrent densities, improved in-plane conductivity, etc. The transportbarrier regions may be conductive or non-conductive or may be composite,comprising conductive and non-conductive regions. Conductivity may referto electrical conductivity or thermal conductivity. If electricallyconductive, the transport barrier regions may be electrically isolatedfrom the active regions. A portion of the one or more transport barrierregions may be electrically conductive, thermally conductive, or acombination thereof, for example. The transport barrier regions may beelectrically insulating, thermally insulating, or combinations thereof.

As used herein, “opened region” refers to a pathway through whichreactant may flow. Opened regions may be holes, vents, slots, panels,pores or a porous material or layer.

As used herein, “electrochemical array” refers to an orderly grouping ofelectrochemical cells. The array may be planar or cylindrical, forexample. The electrochemical cells may include fuel cells, such asedge-collected fuel cells. The electrochemical cells may includebatteries. The electrochemical cells may be galvanic cells,electrolyzers, electrolytic cells or combinations thereof. Examples offuel cells include proton exchange membrane fuel cells, direct methanolfuel cells, alkaline fuel cells, phosphoric acid fuel cells, moltencarbonate fuel cells, solid oxide fuel cells, or combinations thereof.The electrochemical cells may include metal-air cells, such as zinc airfuel cells, zinc air batteries, or a combination thereof.

As used herein, “two-dimensional (2-D) fuel cell array” refers to asheet which is thin in one dimension and which supports a number of fuelcells. A two-dimensional fuel cell array may be a flexible fuel celllayer. A flexible fuel cell layer may be flexible in whole or in part,so-as-to embrace, for example, an electrochemical layer having one ormore rigid components integrated with one or more flexible components.The fuel cells have active areas or active regions of one type (e.g.cathodes) that are accessible from one face of the sheet and activeareas or active regions of another type (e.g. anodes) that areaccessible from an opposed face of the sheet. The active areas may bedisposed to lie within areas on their respective faces of the sheet(e.g. it is not mandatory that the entire sheet be covered with activeareas, however, the performance of a fuel cell may be increased byincreasing its active area.

As used herein, “external environment” or “external conditions” or“environmental conditions” refer to the atmosphere in proximity to thecover, whether that environment resides inside or outside a device orhousing. External conditions include temperature, humidity, pollutant orcontaminant level, for example.

As used herein, “local environment” or “microclimate” or “localconditions” refer to the atmosphere in the proximity of the activeregion(s) of the electrochemical cell array. Such microclimate may bethe environment in which reactant fluids interact with active regions ofan electrochemical cell. For example, the local environment may refer tothe atmosphere in the volume between the active region and the transportbarrier region of the cover. Local conditions may include temperature,humidity, pollutant or contaminant level, for example.

As used herein, “metal-air cells” refer to an electrochemical cellincluding zinc air fuel cells, zinc air batteries or a combinationthereof.

Referring to FIG. 1, a cross-sectional view 100 of a conventionalelectrochemical cell system is shown. The electrochemical cell systemmay include a combination of active regions 106 interspersed withless-active regions 108, disposed on a reactive surface 104. In a planarelectrochemical cell layer, the anodes and cathodes may be disposed onopposing sides of the layer. In a fuel cell, a fuel (e.g. hydrogen,methanol, butane, formic acid) is provided to the anodes (not shown) ofthe fuel cell layer 102, while an oxidant 116 (e.g. air) is provided tothe active region 106 (e.g. a cathode) on a reactive surface 104. Thefuel and oxidant react to form electricity and reaction products 118(e.g. water vapor, CO₂, etc, depending on fuel composition). Fuel cellsoften need some form of external structure to provide support,compression, etc, to ensure proper operation. Since the electrochemicalreaction is dependent on reactant access to the active regions,conventional logic would dictate locating non-porous areas of any suchsupport system or cover away from the active areas of the fuel cells. Asillustrated in FIG. 1, non-porous regions or transport barriers 112 arelocated proximal to less-active regions 108 of the fuel cell array,while opened regions 114 are located proximal to active regions 106 ofthe array. In such a fashion, maximum air access 116 is provided to theactive regions 106 of the array. Further, reactant products 118 caneasily be removed from the reaction sites.

A further consideration for operation of electrochemical cell arrays,such as fuel cell arrays using proton exchange membranes (PEM), is waterbalance. Proton exchange membranes require a certain amount of hydrationin order to facilitate proton transport, as the proton conductivity isinfluenced by the water content of the membrane. However, there must notbe so much water that the electrodes that are bonded to the electrolyteflood, blocking the pores in the electrodes or gas diffusion later. Abalance is therefore needed, between sufficient humidification of themembrane and sufficient evaporation of water from the cathodes. Thisbalance can be difficult to achieve, particularly in passive fuel cells.

Referring to FIG. 2, a cross-sectional view 200 of an electrochemicalcell system, including an off-set cover is shown, according to someembodiments. An electrochemical cell array 202 may include one or moreactive regions 206 and one or more less-active regions 208, disposed ona reactive surface 204. The less-active regions 208 may be in contactwith or surround the active regions 206, or may be interposed with theactive regions 206, and may optionally separate adjacent active regions206. The active regions 206 may alternate with the less-active regions208, for example, such that each active region 206 is adjacent aless-active region 208 on each side of the active region 206. The activeregions 206 may have a width (w) 220. A transport layer 210, which mayalso be referred to as a ‘cover’, may include opened regions 214 andtransport barrier regions 212. In the illustrated embodiment, thetransport barrier regions 212 may be substantially aligned with theactive regions 206 of the electrochemical cell array, while the openedregions 214 may be substantially aligned with the less-active regions208 of the array. In such a configuration, rather than a reactant flow116 having direct access to the active region 106 (as illustrated inFIG. 1), the reactant flow 216 may instead be indirectly provided to theactive region 206 (as illustrated in FIG. 2). In such embodiments, thereactant flow may be directed to the reaction sites of the active region206 along the plane of the active region 206 from the perimeter of theactive region 206, rather than directly contacted with the activeregion.

In the embodiment shown in FIG. 2, the air access to the active areasmay be proportional to the length (into the page) of the active regionand the dimension of the air gap δ 222 and inversely proportional to thewidth w (220) of the active region. By contrast, the air access to theactive area of the array illustrated in FIG. 1 may be proportional tothe length (into the page) of the active region 106 and the width 120 ofthe active region 106. Depending on the dimensions of the active regionand the air gap, air access to the active regions shown in FIG. 2 may bereduced (e.g. relative to the array shown in FIG. 1). Further, transportof oxidant to reaction sites of the active region 206 may occur bydiffusion, rather than convective transport of oxidant. In order for thearray to operate correctly, at least a stoichiometric quantity ofoxidant needs access to reaction sites of the active region; however, itmay be advantageous to limit oxidant access beyond stoichiometricquantities to prevent drying of the membrane.

Modeling results show that the configurations shown in FIG. 2 may havepractical size limits. In an embodiment where the electrochemical cellarray is an air-breathing fuel cell array, and the off-set cover isdisposed in proximity to the cathodes of the array, in order for thefuel cell to still get enough oxygen to operate, equation 1

$\left( {L = \sqrt{\frac{32\; D_{O\; 2}h_{p}{Fc}_{O2}^{o}}{I}}} \right)$

may be used to calculate the oxygen diffusion distance where D_(O2) isoxygen diffusivity, h_(f) is δ 222, F is Faraday's constant (96485 C),c^(o) _(o2) is oxygen concentration at the edge of the transport barrierregion, I is oxygen consumption rate (current density). Current densityand oxygen consumption rate also affect the oxygen availability; athigher consumption rates more oxygen access may be required to supportdevice operation.

FIG. 8 illustrates the maximum distance oxygen can diffuse laterallyunder a solid cover versus the height of the plenum (δ—222 in FIG. 2),assuming the oxygen is diffusing through a space filled with air (asopposed to through a porous layer) and that the current density, I, is125 mA/cm² and oxygen concentration at the edge of the transport barrierregion, c^(o) _(o2), is 0.1.

Referring to FIG. 3, an optional porous intermediate layer 350 may bedisposed between the transport layer 310 and the array 302. The array302 may include a reactive surface 304 in which the active regions 306and less-active regions 308 are supported by or integrated into. Theporous intermediate layer 350 may be positioned between the reactivesurface 304 and transport layer 310. The porous layer may be its owndiscrete entity, disposed on the reactive surface 304 of the array 302,may be integrated into all or part of the reactive surface 304, or maybe integrated into the transport layer 310. If a porous layer isdisposed between the array and the cover, then the modeling resultswould be affected by a different (e.g. lower) diffusivity of fluidthrough the porous layer relative to an open space. Consequently, theaddition of a porous layer may impact the maximum allowable width w(322) of the active region. For instance, if the diffusivity of fluid inthe porous media is lower than the diffusivity of fluid in an openspace, then the maximum diffusive length (and therefore maximum width ofthe active region) would be lower than in an embodiment with no porousmedia between the cover and the cell.

In addition to affecting reactant supply to the electrochemical cell,the cover, including transport barrier region placement and size, openedregion placement and size, and optional porous layer, may further affectremoval of reaction product fluids from the local environment proximalto the array. For example, in an air-breathing fuel cell array, thecover may affect access of oxygen to the cathodes of the array, but mayalso impede removal of product water vapor from the local environment. Aporous layer may provide benefit by affecting diffusivity in the localenvironment, such that sufficient oxygen is provided to the cathodes tosupport the electrochemical reaction, but that diffusion of productwater is inhibited sufficient to provide adequate proton conductivity inthe ion exchange membrane to also support the reaction, but notinhibited to the point that the cathodes of the fuel cell array becomeflooded with too much water.

In another example, the cover may be disposed proximal to the anodes ofa fuel cell array, and may affect rate and quantity of fuel provided tothe anodes.

The porous layer may be manufactured of an adaptable material. Theporous layer may be manufactured of a thermo-responsive polymer. Thepolymer may include a plurality of pores. Adaptive materials included inthe cover can respond to conditions external to the cover, conditions ator near the fuel cells, active control mechanisms, other stimuli, or anycombination thereof. Some examples of conditions include temperature,humidity, an electrical flow, etc. One example of a thermo-responsiveadaptable material is described in U.S. Pat. No. 6,699,611, filed May29, 2001, entitled “FUEL CELL HAVING A THERMO-RESPONSIVE POLYMERINCORPORATED THEREIN,” the disclosure of which is incorporated herein.

The cover may include multiple components or layers. For example, thecover may include a porous layer disposed between a transport layer(having the transport barrier regions and opened regions) and theelectrochemical cells. The cover, the exterior layer, the porous layer,other suitable layers, or any combination thereof may be removableand/or may include an adaptive material responsive to stimuli. Examplesof covers having removable features and adaptive materials are describedin commonly-owned co-pending U.S. patent application Ser. No.12/238,040, filed Sep. 25, 2008, entitled “FUEL CELL COVER,” thedisclosure of which is herein incorporated by reference.

Referring to FIGS. 2 and 3, the cover or transport layer includestransport barrier regions 212, 312 in proximity to active regions 206,306 and opened regions 214, 314 in proximity to less-active regions 208,308 of the electrochemical cells. The transport barrier regions 212, 312may be disposed such that they are substantially aligned with the activeregions 206, 306, or may be disposed such that they are of slightlysmaller width than the active region width (w) 220, 320 or slightlylarger than the active region width 220, 320. In such embodiments, it ispossible that the transport barrier regions 212, 312 may overlap theless-active regions 208, 308. Proportionally, the portion of thetransport barrier region 212, 312 disposed above the active regions 206,306 may be greater than the portion over the less-reactive regions 208,308. The opened regions 214, 314 allow reactants to contact theelectrochemical cell array—the size of the opened regions may be variedto allow more or less reactant access to the array. In some embodiments,the cover can be used to affect transport of an oxidant to the cathoderegions of one or more fuel cells. The transport barrier region 212, 312may align fully with the active regions 206, 306 or overlap the activeregions 206, 306. The opened regions 214, 314 may substantially alignwith the less-active regions 208, 308, or may be smaller or larger inwidth than the less-active regions 208, 308. If the transport barrierregions 212, 312 are electrically conductive, they may be partially orfully electrically isolated from the active regions 206, 306. This maybe accomplished by substantially insulating the transport barrierregions 212, 312 from the active regions 206, 306, insulating thetransport barrier regions 212, 312 from the less-active regions 208, orinsulating the transport barrier regions 212, 312 from at least aportion of either, for example. Transport barrier regions 212, 312 maybe insulated from selected active regions and less-active regions so asto avoid a short-circuit between neighboring cells in an array. It willbe understood by those skilled in the art that there are many variationsin electrical configurations possible (e.g. parallel, serial,combinations thereof), and electrical insulation may be determinedaccordingly.

Referring to FIG. 4, a cross-sectional schematic of an embodimentwherein the porous intermediate layer 452 does not extend across theentirety of the electrochemical cell array 402. It should be understoodthat the schematic is solely for illustrative purposes, and that theporous intermediate layer 452 may be larger or smaller than illustrated,or, alternatively, the porous layer may extend across the width 422 ofthe active regions 406, but have a discontinuity across the less-activeregions 408. While the discussions above reference contacting an oxidantto the cathodes of an electrochemical cell array, the same principlesmay be applied to the contacting a reactant (e.g. fuel) with the anodesof an electrochemical cell array.

Referring to FIG. 5, a perspective view 300 of an electronic devicepowered by an electrochemical cell utilizing an off-set cover is shown,according to some embodiments. An off-set cover 304 may be attached orin contact with an electronic device 302. The cover 304 may includeopenings 306, 308, such as vents, slots or panels. The cover 304 mayinclude a plurality or pores or holes 402 (see FIG. 6).

Panels may be configured into the cover to vary the dimensions of openedregions or openings 306, 308. The cover 304 may also include a porousmaterial, for example. Panels may be provided that modify the apertureof the opened regions or openings 306, 308 (e.g. by sliding across theopened regions) to vary reactant flow between the active regions and theexternal environment. The position of the panels can be varied to adaptto various electrochemical cells having exposed active regions. Forexample, the panels may be positioned to selectively expose portions ofactive areas of electrochemical cells or selectively expose portions ofthe electrochemical cell array. The position of the panels can be useractuated via manual or electronic mechanisms or can be actuated based ondetected conditions. Some examples of conditions for varying theposition of the panels include external environmental conditions,performance of the system, and modes, such as standby or power deliverymodes, of the portable application device.

The electronic device 302 may be a fuel cell powered device. The device302 may be a cellular phone, satellite phone, PDA, smartphone, laptopcomputer, computer accessory, ultra mobile personal computer (UMPC),display, personal audio or video player, medical device, television,transmitter, receiver, lighting device, flashlight or electronic toys.The device 302 may be a refueler, such as an electrolyser, for fuel cellpowered electronic devices, for example. A fuel for a fuel cell may behydrogen, for example, although any suitable fuel such as methanol,ammonia borane, hydrazine, ethanol, formic acid, butane, borohydridecompounds etc. may be utilized.

The cover 304 may be removable or may be integrated into the housing ofthe device 302. One or more transport barrier regions of the cover 304may be integrated into the housing of the device 302, for example.

Referring to FIG. 7, a block flow diagram 700 of a method of operatingan electrochemical cell array is shown, according to some embodiments.An electrochemical cell array may include a reactive surface, having oneor more active regions and one or more less-active regions in contactwith the one or more active regions. The active regions may include acatalyst and an ion-exchange membrane. A cover may include openedregions through which fluids may pass and transport barrier regionswhich are partially or substantially impermeable to fluids. Thetransport barrier regions of the cover may be in proximity to the activeregions of the array and the opened regions of the cover may be inproximity to the less-active regions of the array. The cover and thereactive surface of the electrochemical cell array may define a localenvironment in proximity to the active regions of the array.

Active regions of an electrochemical cell array may be contacted with areactant fluid via opened regions in a cover. Further, a product fluidmay be inhibited from being removed from the local environment proximalto the electrochemical cell through use of the cover.

In the case of a fuel cell array with an ion exchange membrane,inhibiting removal of a product fluid may further result in hydrating orhumidifying the ion-exchange membrane, which may be beneficial foroperation of the array.

Contacting 702 and inhibiting 704 may be passive, such as by diffusion.The reactant may follow an indirect path to the active regions (via theopened regions in the cover), which may lower the velocity of thereactant. Such a reactant flow may be more diffusive than convective,for example.

Contacting 702 the reactant flow with the active regions and inhibiting704 removal of product fluid may be affected, restricted or obstructed.Affecting may include varying the dimension of the opened regions ordirecting the flow of reactant through a porous layer, for example. Ifthe porous layer includes an adaptable material, affecting may includevarying a property of the adaptable material. The property of anadaptable material may be its porosity, for example. Contacting 702 andinhibiting 704 may be varied in response to an environmental conditionin proximity to the electrochemical cells of the array. Theenvironmental conditions may include one or more of a temperature,humidity, or environmental contaminants level.

Contacting 702 and inhibiting 704 may also be varied in response to asignal, for example. For example, the adaptive material may be heated inresponse to a signal. By heating the adaptive material, one or more ofthe adaptive material properties may be varied. In another example, theaperture of the opened regions may be enlarged or reduced in response toa signal.

The performance of the electrochemical cell array may be determinedperiodically or continuously monitored.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples may be used incombination with each other. Other embodiments can be used, such as byone of ordinary skill in the art upon reviewing the above description.Also, in the above Detailed Description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. An electrochemical cell system, comprising: an array ofelectrochemical cells, including a reactive surface, the surface havingone or more active regions and one or more less-active regions incontact with the one or more active regions; and a cover, including atransport layer having one or more transport barrier regions and one ormore opened regions; wherein the transport barrier regions are inproximity to the active regions and wherein the opened regions are inproximity to the less-active regions.
 2. The system of claim 1, whereinthe transport barrier regions are substantially aligned with the activeregions.
 3. The system of claim 1, wherein the opened regions aresubstantially aligned with the less-active regions.
 4. Theelectrochemical cell system of claim 1, wherein the electrochemicalcells comprise fuel cells.
 5. The electrochemical cell system of claim 4wherein fuel cells comprise proton exchange membrane fuel cells, directmethanol fuel cells, alkaline fuel cells, phosphoric acid fuel cells,molten carbonate fuel cells, solid oxide fuel cells, or combinationsthereof.
 6. The electrochemical cell system of claim 1, wherein the oneor more less-active regions separate adjacent active regions.
 7. Theelectrochemical cell system of claim 1, wherein the electrochemicalcells comprise galvanic cells, electrolytic cells, electrolyzers orcombinations thereof.
 8. The electrochemical cell system of claim 1,wherein the electrochemical cells comprise metal-air cells.
 9. Theelectrochemical cell system of claim 1, wherein the one or more activeregions comprise one or more catalysts.
 10. The electrochemical cellsystem of claim 1, wherein the cover is removable.
 11. Theelectrochemical cell system of claim 1, wherein the cover is integratedinto a housing for a portable device.
 12. The electrochemical cellsystem of claim 1, wherein the one or more transport barrier regions aresubstantially impermeable to water.
 13. The electrochemical cell systemof claim 1, wherein the one or more transport barrier regions aresubstantially impermeable to air.
 14. The electrochemical cell system ofclaim 1, wherein at least a portion of the one or more transport barrierregions are electrically conductive, thermally conductive, orcombinations thereof.
 15. The electrochemical cell system of claim 14,wherein the conductive portions of the transport barrier regions areelectrically isolated from at least a portion of the reactive surface.16. The electrochemical cell system of claim 1, wherein the one or moretransport barrier regions are electrically insulating, thermallyinsulating, or combinations thereof.
 17. The electrochemical cell systemof claim 1, further comprising a porous layer.
 18. The electrochemicalcell system of claim 17, wherein the porous layer is disposed betweenthe cover and the array of electrochemical cells.
 19. Theelectrochemical cell system of claim 17, wherein the porous layer isdisposed on the reactive surface of the array.
 20. An electrochemicalcell array cover, comprising: a transport layer, including one or moretransport barrier regions and one or more opened regions; wherein thetransport barrier regions overlay one or more active regions of one ormore electrochemical cells of an electrochemical array.
 21. Theelectrochemical cell array cover of claim 20, wherein the cover isremovable.
 22. The electrochemical cell array cover of claim 20, furthercomprising panels configured to vary the dimensions of the one or moreopened regions.
 23. The electrochemical cell array cover of claim 20,wherein the one or more transport barrier regions are electricallyconductive, thermally conductive, or combinations thereof.
 24. Theelectrochemical cell array cover of claim 20, wherein the opened regionscomprise slots, vents, holes, a porous material, or a combinationthereof.
 25. The electrochemical cell array cover of claim 20, furthercomprising a porous layer.
 26. The electrochemical cell array cover ofclaim 25, wherein the porous layer comprises an adaptable material. 27.The electrochemical cell array cover of claim 25, wherein the porouslayer comprises a thermo-responsive polymer.
 28. The electrochemicalcell array cover of claim 27, wherein the thermo-responsive polymerincludes a plurality of pores.
 29. The electrochemical cell array coverof claim 28, wherein the pores are reduced at higher temperatures.
 30. Amethod for operating an electrochemical cell array, comprising:contacting active regions of an electrochemical cell array with areactant fluid via opened regions in a cover, the electrochemical cellarray including a reactive surface, the surface having one or moreactive regions and one or more less-active regions interposed with theone or more active regions, the cover including opened regions throughwhich fluids may pass, and transport barrier regions which aresubstantially impermeable to fluids wherein the transport barrierregions of the cover are in proximity to the active regions of the arrayand wherein the opened regions of the cover are in proximity to theless-active regions of the array and wherein the cover and the reactivesurface of the electrochemical cell array define a local environment inproximity to the active regions of the array, inhibiting a product fluidfrom being removed from the local environment through use of the cover.31. The method of claim 30, wherein the active regions comprise acatalyst and an ion-exchange membrane, the method further comprisinghydrating the ion-exchange membrane with the product fluid.
 32. Themethod of claim 30, further comprising varying the rate of contactingreactant fluid with the active regions and varying inhibiting productfluid removal.
 33. The method of claim 32, wherein varying the ratecomprises changing the dimensions of the opened regions of the cover.34. The method of claim 32, wherein varying the rate comprises directingthe fluid through a porous layer.
 35. The method of claim 34, whereinthe porous layer comprises an adaptive material.